Citrus Rootstock Named &#39;UFR-17&#39;

ABSTRACT

‘UFR-17’ is a new and distinct allotetraploid citrus rootstock for tree size control and improved disease resistance. ‘UFR-17’ has shown a positive reaction to Huanglongbing disease (HLB, or citrus greening disease) in multiple experimental field trials. Scion trees grafted on this rootstock show a reduced frequency of infection and reduced disease symptoms once infected as compared to commercial diploid rootstocks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/969,678, filed Mar. 24, 2014, herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Latin name of the genus and species of the plant claimed: [Citrus reticulata/Citrus paradisi+Citrus grandis]×[Citrus aurantium+Citrus sinensis/Poncirus trifoliata]

Variety denomination: ‘UFR-17’

The present invention relates to a new and distinct variety of citrus rootstock named ‘UFR-17’. The Plant Improvement Team at the University of Florida's Citrus Research and Education Center (CREC) in Lake Alfred, Fla. has pioneered the development and testing of allotetraploid citrus rootstocks. ‘UFR-17’ (identified as Green #2 in field trials) is an allotetraploid zygotic hybrid derived from a conventional cross of two somatic hybrids previously produced by protoplast fusion. The somatic hybrid seed parent is ‘Nova’ mandarin hybrid+Hirado Buntan pummelo (zygotic seedling), and the somatic hybrid pollen parent is sour orange+Carrizo citrange.

BRIEF SUMMARY OF THE INVENTION

‘UFR-17’ was selected on the basis of its positive reaction to Huanglongbing disease (HLB, or citrus greening disease) in multiple experimental field trials. Scion trees grafted onto this rootstock showed a reduced frequency of infection and reduced disease symptoms once infected when compared to other commercial diploid rootstocks. ‘UFR-17’ is seedy and polyembryonic, making it amenable to standard nursery propagation practices for uniform liner production. Because scion trees grafted onto ‘UFR-17’ grow off quickly and remain small to medium-sized, ‘UFR-17’ has potential use in Advanced Citrus Production Systems that feature high-density plantings. Long-term performance of trees grafted onto ‘UFR-17’ is unknown. Yield and fruit quality data is limited, but 4-year-old trees indicate good productivity in several locations, including ridge and flatwood sites. Tolerance to citrus blight is also unknown, but under investigation. The first asexual reproduction of UFR-17 was performed in Lake Alfred, Fla. by grafting buds of the original tree to Carrizo citrange and Swingle citrumelo rootstocks. Additional true-to-type trees have been propagated from these two grafted trees via rooted cuttings and by nucellar seed propagation.

BRIEF DESCRIPTION OF THE DRAWINGS

‘UFR-17’ is illustrated by the accompanying photographs, which show the tree form, foliage, and fruit. The colors shown are as true as can be reasonably obtained by conventional photographic procedures. The photographs are of a tree approximately 12 years old on Carrizo citrange rootstock growing in Lake Alfred, Fla. All figures were taken in the fall of 2013 from the same tree.

FIG. 1—Shows a close-up of the nearly mature fruits with the rind and cross-sectional view of the fruit when cut in the center.

FIG. 2—Shows the overall mature plant growth habit.

FIG. 3—Shows nearly mature fruits hanging on the tree.

FIG. 4—Shows a close-up of leaves and nearly mature fruits.

FIG. 5—Shows a close-up of nearly mature fruits.

FIG. 6—Shows a close-up of seeds from nearly mature fruit.

DETAILED BOTANICAL DESCRIPTION

The following detailed description sets forth the distinctive characteristics of ‘UFR-17’. The colors (except those in common terms) are described from the R.H.S. Colour Chart published by The Royal Horticultural Society in London (second edition), in association with the Flower Council of Holland.

-   Phenotypic description of Citrus grandis×Citrus reticulata ‘UFR-17’: -   Classification:     -   -   Botanical.—[Citrus reticulata/Citrus paradisi+Citrus             grandis]×[Citrus aurantium+Citrus sinensis/Poncirus             trifoliata].         -   Common name.—Complex allotetraploid ‘tetrazyg’ rootstock             hybrid. -   Parentage:     -   -   Female parent.—‘Nova mandarin+Hirado Buntan zyg.’ somatic             hybrid (unpatented).         -   Male parent.—‘Sour orange+Carrizo citrange’ somatic hybrid             (unpatented). -   Tree:     -   -   Ploidy.—Tetraploid.         -   Size.—Medium.         -   Height.—3.5 meters.         -   Tree spread.—3.5 to 4.0 meters.         -   Vigor.—Vigorous.         -   Density.—Canopies are quite dense.         -   Form.—The tree is obloid-shaped with most lateral branches             growing toward low to medium angles.         -   Growth habit.—Tree exhibits both upright and lateral growth. -   Trunk:     -   -   Trunk diameter.—16.5 cm in diameter at 30 cm above the             ground on a 12-year-old tree grafted to Carrizo citrange             rootstock.         -   Trunk texture.—Smooth.         -   Trunk bark color.—RHS 197A (greyed-green); irregularly             striated with RHS N189 (greyed-green). -   Branches:     -   -   Crotch angle—First crotch forms a 40- to 45-degree angle;             middle crotch forms a 90-degree angle.         -   Branch length—Branch reaches 2.6 meters from the first             crotch to the tip of the branch.         -   Branch texture.—Relatively smooth with occasional small             thorns or spines.         -   Branch color (shoots from previous flush, hardened, and 4 to             5 mm in diameter).—RHS 137A (green). -   Leaves:     -   -   Size (lamina average).—Length: 90.5 mm Width: 61.6 mm L/W             ratio: 1.46.         -   Thickness.—Thicker than average diploid citrus rootstock             hybrids.         -   Type.—Mostly simple leaf types, occasionally with bifoliate             types of leaves appearing within the same tree.         -   Shape.—Elliptical.         -   Apex.—Retuse.         -   Base.—Acute to sub-obtuse.         -   Margin.—Entire and slightly undulate.         -   Surface.—Upper surface: Glabrous Lower surface: Medium veins             that are pinnately netted.         -   Color.—Upper surface (adaxial): RHS N137A (green) Lower             surface (abaxial): RHS 146A (green).         -   Petiole.—Shape: Brevipetiolate (shorter than leaf lamina);             junction between petiole and lamina is articulate Width             (petiole wing): Narrow Shape (petiole wing): Obovate Length:             21.6 to 24.6 mm Width: 5.6 to 6.7 mm Color: RHS N137A             (green). -   Flowers and flower buds:     -   -   Type.—Hermaphrodite.         -   Bearing.—Flowers grow from leaf axillaries and leaf             terminals singly and in small clusters; most single flowers             grow from leaf axillaries.         -   Flower bud size.—Shape: Initial visible flower bud has a             round ball shape; mature flower buds have an elongated olive             shape.         -   Flower petals.—Shape: Flat, spatula-shaped Apex shape:             Smooth, acute-shaped Base shape: Even obtuse Margin: Smooth.         -   Flower sepal.—Shape: Delta-shaped Apex shape:             Triangle-shaped Margin: Smooth.         -   Fragrance.—Fragrant/Mostly fragrant.         -   Reproductive organs.—Fertility: Appears self-fertile Pollen             amount: Abundant/moderate amount Pollen color (general):             Bright-yellow Ovary shape: Oval-shaped. -   Fruit:     -   -   Size.—Uniform.         -   Height.—77 to 83 mm on average.         -   Width.—88.2 to 90 mm on average.         -   Average weight (per individual fruit).—275 grams.         -   Shape.—Round.         -   Shape (cross-section).—Round.         -   Apex.—Truncated with slight dent.         -   Apex cavity diameter.—N/A.         -   Base cavity diameter.—5.8 to 7.0 mm.         -   Base—No neck.         -   Harvesting.—Fruit can be harvested from October through             December in Florida, although fruit continue to hold on the             tree for a longer time.         -   Fruit stem (short stem connecting the fruit).—Length: 10 mm             Diameter: 5.6 mm Color: RHS 197A (greyed-green) with RHS             138C (green) strip. -   Rind:     -   -   Adherence.—Adherence between albedo (mesocarp) and flesh             (endocarp) is medium. The adherence is evenly distributed             from base to apex.         -   Thickness.—3.4 to 3.8 mm on average.         -   Texture.—Smooth.         -   Color.—Flavedo (epicarp): Ranges between RHS N144B             (yellow-green) to RHS 150C (yellow-green) Albedo (mesocarp):             RHS 155C (white).         -   Stylar end.—Closed.         -   Rind oil cell density.—100-105 oil cells/square cm. -   Flesh:     -   -   Number of segments.—Between 10 and 11 segments per fruit on             average.         -   Segment walls.—Medium-soft with sufficient strength to             maintain integrity as separated.         -   Juice.—Abundant.         -   Color.—Uniformly RHS 151D (yellow-green).         -   Texture.—Medium soft.         -   Vesicles.—Length: Arranged from 14.2 to 15.6 mm on average             Diameter (thickness): 3.8 to 4.6 mm on average.         -   Eating quality.—N/A.         -   Juice index.—         -   Soluble solids (average).—9.2 Brix. -   Seeds:     -   -   Type.—Polyembryonic and monoembryonic.         -   Number.—Ranges from 18 to 26.         -   Shape.—Seed shapes are not uniform. Normal seeds are mostly             ventricose/swollen-shaped and clavate/club-shaped.         -   Size.—Length: 15 to 21.5 mm Width: 8.5 to 10.9 mm.         -   Seed coat color.—Outer Surface: RHS 155A (white) and             wrinkled Inner surface: RHS 165B (greyed-orange) Cotyledon             color: RHS NN155A (white). -   Resistance to disease: ‘UFR-17’ rootstock was selected on the basis     of its positive reaction to HLB disease (huanglongbing or citrus     greening disease) in multiple field trials. Trees on this rootstock     show a reduced frequency of infection and reduced disease symptoms     once infected as compared to commercial diploid rootstocks. 

What is claimed is:
 1. A new and distinct citrus rootstock cultivar as illustrated and described herein. 